The patient is a female, 31 years old. She came to our hospital due to chest tightness and breath-holding after recent activities. Chest X-ray plain film and CT suggested: a large amount of fluid in the right thoracic cavity (Figure 1). Ultrasonic chest exploration: a large amount of liquid dark area in the right chest cavity, occupying the whole right chest cavity, with slightly poor sound transmission, suggesting the same X examination. It was decided to perform ultrasound-guided aspiration treatment of the right pleural effusion and send fluid for laboratory examination. During puncture, the needle was felt to have resistance in the thoracic cavity, and no fluid was extracted, followed by puncture biopsy, which detected solid tissue and pathological diagnosis: nodular neuroblastoma. Surgery confirmed that the huge tumor originated from the posterior mediastinum and protruded into the right thoracic cavity, and the lung lobes were compressed and squeezed into the upper part of the thoracic cavity in a narrow space with poor development, and the whole thoracic cavity was almost completely occupied by the tumor. The tumor was peeled off and excised completely. The texture was soft, and the tumor tissue was fatty colored to the naked eye. The envelope was intact, and sparse, thin blood vessels could be seen distributed in the inner part of the envelope, weighing 4200 g. Discussion Nodal neuroblastoma is a benign cell tumor that can grow in any part, mostly in the thoracoabdominal sympathetic chain, protruding outward in the paravertebral sulcus, and growing slowly. Nodular neuroblastoma has a large, soft, hypotonic, and intact envelope. Pathology reveals myelinated nerve fibers with scattered clusters of abnormal ganglion cells, differentiated areas with neuronal cells, and more fluid between cells. The reasons for the misdiagnosis of this case by ultrasound were analyzed as follows: 1. The tumor was huge, occupying the whole thoracic cavity, with no referable tissue echo, and the fluid movement sign could not be observed. 2.Rashly listening to the misleading CT diagnosis, without carefully observing and analyzing the ultrasound images again. After biopsy and careful analysis of the images, scattered fine dotted echogenicity was still visible in the dark area, with still uniform distribution and poor sound transmission (Figure 3); sparse and fine arterial blood flow signal could be seen in color Doppler examination (Figure 4). Therefore, if the ultrasound images are carefully observed and analyzed, it will not be easily misjudged as pleural effusion. 3. The pathological characteristics of the tumor are easy to be misinterpreted as pleural effusion. Nodular neuroblastoma has more intercellular fluid components, less acoustic reflection and lower echogenicity is also a reason for easy misdiagnosis. 4. The cases are rare and doctors lack clinical experience. In fact, ultrasound examination is better than CT examination in the differentiation of substantial occupancy and large amount of fluid. In conclusion, the main reason for misdiagnosis is the low echogenicity of nodular neuroblastoma itself. Figure 3 Two-dimensional ultrasound image of right thoracic giant nodal neuroblastoma with fine dotted echogenicity